Open it · Which databases, and their limits
What is in it
Elements. Properties, with sources, arranged so that the periodic trends are visible rather than tabulated.
Material classes. Metals, ceramics, polymers, composites, semiconductors — what defines each, how their property ranges differ, and where the boundaries are conventions rather than physics.
Crystallography. Lattice systems, space groups, common structure types, and what the notation means when a database hands it to you.
Search across open databases. One query against the OPTIMADE federation — Materials Project, OQMD, AFLOW, COD, JARVIS and the rest. Roughly 27.3 million structures across 45 aggregated sub-databases, from 21 registered providers. The full source list.
What you should know before trusting a number here
Most of what the knowledge base surfaces is computed, not measured, because that is what the open databases hold. Under the E-ladder a DFT value quoted with its entry identifier and functional is E2 — reproducible in principle, not a measurement.
The errors are systematic and quantified. Computed band gaps run about 40% low by the Materials Project’s own account; formation energies carry errors near 100 meV per atom depending on the functional. Structures and geometry are far better predicted than energetics. The numbers, with sources.
None of this makes the data less useful. It makes it useful for particular things — screening, trends, structures, comparisons — and unsuitable for others, particularly anything that reaches a drawing as an allowable.
Why it is free and unlimited
Two reasons, and neither is generosity.
The underlying data is public and free. Charging for lookups against databases that LBNL and Northwestern maintain with public money would be charging for someone else’s work, and the attribution requirements in those licences exist for a reason.
And it is the honest place to start. If you want to know whether our citations hold up, the place to test that is a lookup where you already know the answer — free, unlimited, no card.
What is metered is the work we actually do: the research agent, the Selector, and the reports they produce. Pricing.
What this page does not cover
- Measured engineering properties of commercial grades. Not present. The open databases are indexed by composition and crystal structure, and a grade designation is a specification. Why that gap exists.
- Polymers, composites and formulated materials. Outside the data layer.
- Experimental crystal structures at ICSD or CSD depth. Both are commercial; the open Crystallography Open Database is reachable and is not a substitute.
- Offline or API access. Not available.